Cube polarizing beam splitters (PBSs for plural or PBS for singular) can be used to polarize a beam of light and split it into two, oppositely-polarized light beams. The effectiveness or performance of a cube PBS can be based on a fraction transmission of a predominantly-transmitted polarization (e.g. Tp), a fraction transmission of a predominantly-reflected polarization (e.g. Ts), and a fraction reflection of the predominantly-reflected polarization (e.g. Rs).
Users of PBSs often desire one or more of the following: high contrast (Tp/Ts), good performance across a large range of incident angles, and good performance across a large wavelength range. It is difficult to provide a cube PBS to satisfy all of these desires.
Another desirable aspect of a cube PBS is symmetry, meaning equality of an optical path length of a transmitted polarization and an optical path length of a reflected polarization.